1. Technical Field
Priority is hereby claimed to Japan Patent Application No. 2012-213286 filed on Sep. 26, 2012, and such priority application is hereby incorporated by reference herein, in its entirety. The present invention relates to an optical modulator and in particular, relates to an optical modulator that compensates for wavelength dispersion of an optical fiber transmission line.
2. Background Art
In the field of optical communication and the field of optical measurement system, light waves modulated by an optical modulator are transmitted using optical fibers. Since, the propagation speed and the length of a propagation pathway of light differ according to the wavelength in an optical fiber, wavelength dispersion occurs and the wavelength of optical signals is distorted. Therefore, technology that compensates for wavelength dispersion of an optical fiber transmission line is essential ire the high-speed communications that exceeds 40 Gbps, the high-speed transmission systems of wavelength multiplexing and the like.
As methods of compensating for wavelength dispersion, there are methods that dispose dispersion compensation fibers immediately prior receivers of optical signals, and use optical devices such as the fiber Bragg grating (FBG) and etalon of Patent Document 1, and furthermore, there are methods that use a digital signal processing circuit such as those of Patent Document 2 and Non-Patent Document 1. In the method using digital signal processing circuits, an impulse response, which corresponds to changes in real parts and imaginary parts with respect to wavelength dispersion and performs compensation with a digital signal processor, is generated.
In the method using dispersion compensation fibers, the degree of accuracy of the compensation is limited by the smallest unit of the compensation amount thereof, and in addition, since wavelength division multiplexing (WDM) light or the like is separated in the compensation for wavelength dispersion of WDM light or the like, an optical device such as an FBG that functions as a wavelength dispersion compensating device or the like is also necessary. Furthermore, in addition to the fact that there is a limit to the bands of wavelength that optical devices such as FBGs can handle, there is a large amount of optical loss. Additionally, in digital signal processing circuits, there is a problem in that high-speed processing that exceeds 40 Gbps is technically difficult.